US1986450A - Thermionic tube - Google Patents

Description

P. F. SCOFIELD THERMIONIC TUBE Jan. -1, 1935.

Filed July 18, 1932 INVENTOR,

HIL/P F. SCOF/ELD. wfw

ATTORNEY Patented Jami, 1935 rnm vnomo TUBE Philip F. Scofield, Palo Alto, Calif., assignor to Heintz & Kaufman, Ltd., San a corporation of Nevada Francisco, Calif.,

Application July 18, 1932, Serial No. 623,115

2 Claims. (01. zan -27.5)

My invention relates to a thermionictube having a variable amplification factor, and more, particularly to such a tube inwhich a wide rib-, bon filament is positioned between a control 'electrode and the anode, the. fiat surface ofthe ribbon being at'right angles to the plane of the control electrode. t r I Amongthe objects of myinvention are: To'pro-' vide a thermionic tube having a variable mu.- factor or amplification factor; to'provide a vari-' able mu tube of simple and economical construction; to provide a thermionic tube having a mufactor which varies from point to point of the cathode emissive surface; and to provide avariable mu tube designed for the eliminationofdistortion in radio receiving sets. r I

Other objects of my invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of my invention herein described, as various forms may be adopted within the scope of the claims.

Referring to the drawing: i

Figure 1 is a view, partly in section and partly i. in elevation, of a vacuum tube embodying this invention.

, Figure 2 is a cross sectionalview taken in the plane indicated by the line 2-2 in Figure 1.

Figure 3 is a longitudinal section of the elements alone, taken in a plane indicated by the line 3-3 in Figure 2. y

In broad terms my invention comprisesa thermionic tube having an anode and control electrode, preferably located in parallel planes. A cathode comprising a wide ribbon filament is 1 positioned between the electrodes, with one narrow edge close to and parallel to the control electrode. The major surface of the ribbon is preferably at right angles to the plane of the control electrode. In the drawing, which represents a preferred embodiment of my invention, a bulb 1 is proported respectively by'the anode supports. '7 and the control electrode supports 9. One of each of these supports may be a dummy, or a support which does not extend all the way through the pinch. v

The anode and control electrode are preferably a formed as fiat plates, provided with flanges'lo for stiffening purposes, and made of nickel, or tantalum. i It is customary to fasten such plates -to the support wires byQelectric welding.

A bridge support 11 extends upwardly from the top of bothanode and control electrode and is inserted into a filament bridge 12 of insulating material such as lava or isolantite, which serves ,both to space and maintain the plates and 6 parallel, and to providea bearing hole 14 through ,which is placed a filament hook 15.

The shank 16 of this hook is inserted into an extension spring 1-7 fastened to the shank by the weld 19.

Filament leads '20, both extending through the of ,a lwide invertedV-shaped ribbon filament 21 i which has its apex 22 caught by the filament hook so that the entire filament is firmly held in tension by the spring 17. V

The filament leads are bent and adjusted until one narrow edge of the ribbon is close to the control electrode and equally spaced from it. At the same time the wide surface is positioned at right angles to the plane of the control electrode.

Afterthese adjustments'have been made the tube is exhausted and. sealed off the pumps in the usual manner, and provided with a base 24. The lead wires 25 coming from the electrodes are inserted' into base prongs 26 in the customary order and. secured to the prongs by soldered joints 2'7.

In operation as used in conjunction with the proper circuits to take advantage of its variable mu characteristics, the control electrode will have a high degree of control over the emission from that portion of the ribbon closest to the electrode, and a lesser degree of control over the emission from the far portions of the cathode ribbon. The variation of mu-factor may be increased by increasing the width of the ribbon.

I am. aware of the fact that ribbon filaments have been used in ordinary tubes in edge relation to the electrodes, but in all such cases the ribbon has been made very narrow so that uniform control might be had of all the emission. I deliberately utilize a wide ribbon, and with such wide ribbons a wide variation in mu-factor may be ;obtained. The advantages of a high amplification factor are retained at normal voltages, while at high biases, the low distortion characteristics .ed to three-element tubes, it is obvious that the same general results andadvantages will be obtained when used in conjunction with tubes having additional control, accelerating or shielding 2. Means for producing a variable mu factor in electrodes. a thermionic tube comprising an anode, a control I Olaim! electrode, and a wide ribbon filament interposed A thermionic tube comprising an anode between said anode and cathode, one narrow edge control electrode and cathode having flat of said ribbon being closer to said control elecemissive surface interposed between said anode tmde than the other narrow edge and control electrodes, and having its narrow electrode.

- edge closely adjacent and parallel tothe control I :1 I I r v EPHILIP F SCOFIELD

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